The object of the present invention is an electrostatic charge de-ionizing lightning rod aimed at optimizing the protection of wind turbines against lightning action, specifically designed to reduce direct lightning impact over the blades of wind turbine generators.
The object of the present invention is also to provide a wind turbine generator with blades having the electrostatic charge de-ionizing lightning rods of the invention.
The present invention is related to on Spanish patent ES 200202884 in regard to protection against lightning action.
There are several protection systems against lightning action, mainly located on the extremes of the wind generator blades, generally based on air excitation thanks to the power of the tips within a natural electric field, during a storm, to capture lightning, in order to divert it or lead it to a ground circuit.
These systems are unable to guarantee a complete protection to people or facilities as they are unable to control the polarity of lightning or to determine the intensity of the energy that will develop during the operation of the tip lightning rod.
When lightning impacts the tip of the lightning rod, there will be, depending on its polarity, electro-dynamic, thermal, electrical, magnetic and electro-magnetic effects. If lightning polarity is positive, an ascending light trajectory in the direction of the cloud will be physically observed, lightning will come from the wind turbine generator's blade towards the cloud to discharge in it.
In this case, the effort and work executed by this meteorological phenomenon (positive lightning) causes the destruction of material and, to a lesser extent, of electric equipment, since as lightning energy passes through in a fraction of a second it generates a thermodynamic work effort accompanied by instantaneous thermal effects, which transform in the segregation of part of the tip of the blade, causing a fire risk.
The blade then usually loses its aerodynamic properties; it starts vibrating and it eventually gets disengaged from its housing and is expelled, in some cases over a hundred meters away. When the blade is disengaged, the wind turbine generator becomes de-stabilized losing its vertical center of gravity, causing a sudden increase in pressure on the opposite end that can fold and laterally demolish the entire wind generator, all that taking into account of the weight (almost 8000 kg.) and dimensions (an average of around 36 meters) of each of the blades of a wind turbine self-generator.
In case of a negative impact of lightning over the blade, its trajectory will be descending from the cloud to the point of contact with the blade. The effects shown on the blade due to the impact of lightning will be direct and indirect, starting at the tip and ending on the ground circuit that will evaporate its water with loss of the mineral and crystallization of the earth compounds.
As lightning advances over the equipment, its intensity will affect the materials of which the blade is composed. In the point of lightning impact on the blade, an instant direct fusion occurs with loss of material and risk of fire. During this same instant, the current that appears has the high-frequency behaviour that generates, as it passes for an instant, the molecular modification of materials. This effect of the electricity generates the creation of a high intensity electric field that polarizes all material instantly as it passes through. The different electromagnetic phenomenons cause the crystallization of the simplest materials, such as carbon fiber.
These effects generate, in the short term, a loss of mechanical resistance of the materials where the lightning current flows, resulting in an instant change of its physical characteristics, losing their flexibility and the mechanical resistance for which they were designed. The lightning current follows its path, seconds later, through the lower electrical resistance conductors, generating high temperatures and electric arcs, if correct bonding between conductive and semi-conductive materials, such as resin, copper plate, conductive tape, mechanical structure and electric components is not present.
As lightning current advances through the blade, it passes directly to the compartment area of the generator through the conductors or the spark gaps. If the discharge is of great intensity it does not flow through curved conductors, jumping as a spark in a straight line, from the blade's electric conductor towards the rotor's axis, passing the current to the self-generator itself.
The electromagnetic effects due to the lightning impact and the current originate, as they pass through, couplings and inductions on the navigation electronics, which are in charge of the orientation of the self-generator based on the direction of the wind, losing temporary or permanent information, likewise directly affecting the electronic part that regulates braking, which could, after this moment, dangerously increase the generator's speed due to storm winds, reaching the overheating limits of the rotor's bearings as the blade's revolutions increase to their maximum limits.
This overheating can cause a fire of the oil in the aforementioned bearings, at which moment the generator enters a phase referred to as of “sacrifice” due to the velocity of these occurrences and the lack of necessary time for the disconnection of the generator from the grid, making it impossible to use water for the extinction as voltage is present on the set.
Once the fire has initiated in the generator compartment, it extends to the blades, which will detach in pieces, with the generator becoming destroyed, in a vertical or folded position, depending on the circumstances, finally generating losses in production and repair, with very high cost.
As conclusion for this description of the effects of lightning impact and the current protective techniques, it should be stated that the different protective systems placed on the blades have a pointed end and do not provide an effective protection. Currently there are no protection systems that eliminate or limit the possibility of lightning impact on the blade, said systems being conceived for the capture of the lightning through excitation, channeling the lightning to the ground through tips.